The present invention relates to a structure for fitting rocker arms in a mechanism for actuating valves of an internal combination engine.
In general, there are two valves for each cylinder: an intake or inlet valve and an exhaust valve. The intake valve opens during the intake stroke to admit the air-fuel mixture into the cylinder. The exhaust valve opens during the exhaust stroke to permit the burned gases to be exhausted from the cylinder. A mechanism for actuating the valves is related to a crankshaft so as to cause the valves to open and close with the proper relationship to the piston strokes. In the past, various types of valve-actuating mechanisms have been used for internal combustion engines. For example, a side-valve type, over-head valve type and over-head-camshaft type are well known.
FIG. 1 shows an example of conventional overhead camshaft type mechanism. A camshaft 2 is located near a cylinder head 1 and rotates in response to rotation of a crank shaft (not shown). A cam 3 is attached to the camshaft 2 in such a way that it can actuate rocker arms 4 so that the rocker arms move reciprocatively. The rocker arms 4 further actuate intake and exhaust valves 5, 6 so that the valves 5, 6 can open and close during reciprocating action of a piston (not shown).
As shown in FIG. 2, each rocker arm 4 has a boss portion 4' rotatably set onto a rocker shaft 7 which is mounted through a bracket 9 to a support member 8 fixed to the cylinder head 1. The bracket 9 is fixed to the support member 8, for instance, by means of a bolt.
In the illustrated conventional mechanism, two rocker shafts 7 are used. One rocker shaft 7a is equipped with a rocker arm 4a for the intake valve 5. The other rocker shaft 7b is equipped with another rocker arm 4b for the exhaust valve 6. The length of the bracket 9 in the axial direction of the rocker shaft is predetermined in such a manner that the rocker arms 4 can fittably contact both ends of the bracket 9 whereby the position of the rocker arms 4 can be properly located. In order to prevent the rocker arms 4 from moving out of position, also, the rocker shafts 7 are inserted into coil springs 10 between the rocker arms 4 and the brackets 9' adjacent thereto. Thus, the rocker arms 4 are pressed against the ends of the brackets 9'.
However, in such a conventional mechanism for securing the rocker arms 4, before the rocker shafts 7 are fixed to the support member 8, it is necessary to assemble in order the rocker arms 4, coil springs 10 and brackets 9 onto the rocker shafts 7. For such a reason, the assembling efficiency is extremely low. In addition, the brackets 9, coil springs 10 and others are required to be used for the purpose of holding the rocker arms 4 in position. As a result, many parts must be used and the production costs increase.